<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<style>
  .left {
    height: 100px;
    width: 100px;
    float: left;
    background: lightblue
  }

  .right {
    height: 300px;
    background: #eee;
    overflow: hidden;
  }
</style>

<body>
  <div class="left">我是一个左浮动的元素</div>
  <div class="right">我是一个没有设置浮动, 也没有触发 BFC 元素</div>
</body>

</html>